pyaudio OSError: [Errno -9998] Invalid number of channels (On mac with External sound card)

Question

I am writing a python program to stream data from a sound card. It works perfectly when I select the internal mic or the external mic, but won't work with an external stereo sound card (TI PCM2900C).

I have tried both 1 and 2 channels as well as different sample rates, but the error persists.

My input devices are:

0: USB AUDIO CODEC

1: External Microphone

2: iMac Microphone

Devices 1 & 2 work fine, but device 0 gives the error.

p = pyaudio.PyAudio()

# Open the selected audio input device
stream = p.open(
    format=pyaudio.paInt16,
    channels=2,
    rate=48000,
    input=True,
    input_device_index= 0,
    frames_per_buffer=1024)

Changing the channel numbers to 1 or 2 does not make any difference nor does changing the sample rate.

I tried...

# Get the number of channels that the selected device supports
device_channels = p.get_device_info_by_host_api_device_index(0, device_index).get('maxInputChannels')
print('Input device channels is ', device_channels)

It returns "0" for device "0" even though it is a stereo CODEC.

Answer 1

I solved this problem, it turns out that some audio devices have separate indexes for input and output channels. In my instance the USB AUDIO CODEC shows up with indexes 0 and 1.

{'index': 0, 'structVersion': 2, 'name': 'USB AUDIO  CODEC', 'hostApi': 0, 'maxInputChannels': 0, 'maxOutputChannels': 2, 'defaultLowInputLatency': 0.01, 'defaultLowOutputLatency': 0.004354166666666667, 'defaultHighInputLatency': 0.1, 'defaultHighOutputLatency': 0.0136875, 'defaultSampleRate': 48000.0}
 
{'index': 1, 'structVersion': 2, 'name': 'USB AUDIO  CODEC', 'hostApi': 0, 'maxInputChannels': 2, 'maxOutputChannels': 0, 'defaultLowInputLatency': 0.0057083333333333335, 'defaultLowOutputLatency': 0.01, 'defaultHighInputLatency': 0.015041666666666667, 'defaultHighOutputLatency': 0.1, 'defaultSampleRate': 48000.0}

As I was selecting device index 0 (Output) I was getting an error because the number of input channels was zero.

Just make sure you list all devices before selecting the input.

Hope that makes sense.